Communication of data like e.g. speech audio or video data between terminals is usually performed via encoded data streams sent via a communication network. Examples for terminals are mobile phones but also computing devices capable of communication like Personal Computers (PC) or Laptops. Data streams can be communicated via circuit and/or packet-switched communication networks and are to be understood as a medium carrying the data that is to be transferred from a sending terminal to a receiving terminal. Data streams may be composed of individual packets, frames or messages that can be communicated e.g. in a consecutive manner.
To communicate an encoded data stream from a sending terminal to a receiving terminal, the data stream is first encoded at a certain encoding mode by an encoder of the sending terminal. The encoding by an encoding mode, also known as codec or coding format, is usually performed in order to compress the data and to adapt it to further requirements for communication like e.g. encryption. The encoded data stream is sent via the communication network to the receiving terminal where the received encoded data stream is decoded by a decoder for a further processing by the receiving terminal, e.g. outputting a speech signal or playing out a video signal to a user of the receiving terminal. This end-to-end communication fails if the encoder of the sending terminal and decoder of the receiving terminal are incompatible or if the communication network or parts thereof are at least temporarily not capable of transporting the encoded data stream.
A transcoder is a device that performs a conversion of an encoded data stream encoded at a first encoding mode to a corresponding encoded data stream encoded at a second encoding mode. Thus, in case of incompatible encoder/decoder pairs in the sending/receiving terminals and/or in case of communication network capability problems, one or more transcoders can be installed in the communication network such that the encoded data stream can be transferred via the communication network to the receiving terminal and the receiving terminal is adapted to decode the received encoded data stream.
Communication network capability problems are not unlikely on a radio link in a wireless communication network. The radio link is susceptible to congestion, coverage, or hand-over-problems that all put a limit on the currently available transmission bit rate. Thus, for sending an encoded data stream encoded at an encoding mode of a higher bit-rate to a wireless receiving terminal, a switching to an encoding mode of a lower bit rate can be required in case the transmission capability of a wireless link degrades. End-to-end communication from the receiving terminal to the sending terminal to instruct the sending terminal to switch the encoder to an encoding mode of lower rate is often unwanted or even impossible such that one or more transcoders in the communication network must be employed to convert the encoded data stream encoded at an encoding mode of higher bit rate as received from the sending terminal to an encoded data stream encoded at an encoding mode of lower bit rate such that the receiving terminal can receive the encoded data stream at lower bit rate via the problematic radio link and subsequently decode it.
Transcoding typically means decoding an encoded data stream encoded with a first encoding mode and than encoding the decoded data stream according to a second encoding mode. In the process of transcoding encoding parameters that represent the encoded data stream are processed and altered according to pre-defined, often standardized, algorithms, to form a completely new set of encoding parameters that represent the encoded data stream at the second mode. However, such full transcoding wherein all encoding parameters are newly computed consumes a lot of computational power and introduces delays due to the computational load, which is detrimental especially for real- or quasi-real-time communications like e.g. speech or video or audio play-outs or combinations thereof.